Determining Viral Shedding Duration in Patients With SARS-CoV-2: Is Repeat Viral RNA Testing Effective?

Medical worker working in laboratory
SARS-COV-2 pcr diagnostics kit. Medical worker working in laboratory with pipette and reagent for coronavirus testing behind fume hood
Researchers conducted a study to assess whether viral RNA testing is effective in determining the duration of viable viral shedding among patients with severe SARS-CoV-2 infection.

Results of a systemic review showed that repeat viral RNA testing is ineffective in determining the duration of viable viral shedding among patients with SARS-CoV-2 infection. These findings were published in the Journal of Infectious Diseases and Epidemiology.

Researchers searched Medline and Google Scholar databases for case reports, case series, cross-sectional, cohort, and randomized controlled trials published between March and August 2020 that assessed the duration of shedding of viable SARS-CoV-2 virus. Overall, 15 studies comprising 2604 patients were included in the final analysis. Of these studies, 3 were performed in China, 7 in Europe, and 1 each in the United States, Canada, the United Kingdom, Taiwan, and Australia. The researchers noted that 10 studies enrolled hospitalized patients and none of the included studies enrolled children.

In regard to viral culture specimen testing among the 15 studies included in the analysis, 10 used nasopharyngeal, oropharyngeal, and/or sputum samples; 4 used only nasopharyngeal samples; and 1 used only saliva samples.  Most of the data from these 15 articles showed that the last day of successful viral isolation ranged between 7.37 to 15.30 days, with a mean of 11.33 days and median of 9 days.

In 4 studies that included patients treated with either hydroxychloroquine or azithromycin, the number of patients with detectable SARS-CoV-2 viral loads was decreased after 3 or more days of treatment. In addition, 1 study showed that the number of patients with detectable viral loads was decreased following treatment with remedisivir. In regard to the relationship between cycle threshold value (CTv) and detectable SARS-CoV-2 viral load, the researchers noted that 95% of viable specimen samples had a CTv of less than 38 and a median CTv of 34.

Study limitations included heterogeneity across the included studies, as well as the inclusion of studies which did not assess the relationship between CTv and viral load.

According to the researchers, data from these studies suggest that “CTv is insufficient [for identifying] samples with viable virus in patients with severe SARS-CoV-2 infection, and viral replication is best demonstrated by viral culture.” In addition, “further studies regarding SARS-CoV-2 transmutability dynamics are needed, especially in this post-vaccination era [of the COVID-19 pandemic],” the researchers concluded.


Qutub M, Bahabri N, Mehdawi F, et al. Duration of viable SARS-Cov-2 shedding from respiratory tract: A systemic review of available literature. J Infect Dis Epidemiol. 2021;7:227.